• 전기학회논문지P
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• 제63권4호
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• pp.322-326
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• 2014

Recently, the LOE(loss of excitation) incidents are occurred in domestic synchronous generator frequently, the synchronous generator protection system has been much attention for the LOE protection of the incidents that threats synchronous generators and power systems. This paper was showed the characteristics and practices of distance relay that widely used LOE protection relaying in generator. Firstly, the operating characteristics and the impedance locus for LOE of the generator protection were introduced. Even if the conventional simulation program is used for modeling, but it is difficult to implement a LOE modeling and simulation of synchronous generator. So, the LOE relay operation data collected from thermal power plant and nuclear power plant in real fields were analyzed. By reviewing the applications of GE Mho relays, the reliability of LOE for synchronous generator protection in domestic were improved.

• Journal of Electrical Engineering and Technology
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• 제10권4호
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• pp.1453-1459
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• 2015

Loss of excitation (LOE) relay is prevalently used to protect synchronous generator. The widely used method for synchronous generator LOE protection is a negative offset mho relay with two zones. The basis of this relay is identical to mho impedance relay. In other words, this relay calculates impedance by measuring voltage and current at the generator terminal. On the other hand, the presence of series compensation, changes measured voltage and current signals during loss of excitation. This paper reveals that the presence of series compensators such as fixed series capacitors (FSCs) and static synchronous series compensator (SSSC) causes a significant delay on the performance of generator LOE relay. It is also shown that the presence of SSSC causes the LOE relay to be under-reached. Different operating modes of the power system, the SSSC and also different percentages of series capacitive compensations have been considered in the modeling. All the detailed simulations are carried out in the MATLAB/Simulink environment using the SimPowerSystems toolbox.

• 자원리싸이클링
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• 제14권3호
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• pp.63-67
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• 2005

최근 고품위 TV 및 고정세도 디스플레이용으로 화상의 정세도를 향상시키기 위해 수평주파수를 높이려는 경향이 있어, 편향 요크용 페라이트 코아에는 고주파수 영역에 있어서도 코아로스가 낮은 재료가 요구되고 있는 실정이다. Mg-Zn 페라이트에 있어서 화학조성 및 프로세스가 미세구조에 미치는 영향에 착안하여 저온 소결화를 하였다. 저손실인 Mg-Zn계 te에 Cu에 첨가하였다. MgO, ZnO, Fe$_2O_3$, CuO를 선택한 후 조성비의 변화를 두며 CuO를 MgO로 치환하였다. 이 시료를 980$^{\circ}C$~1350$^{\circ}C$까지 3시간 소결하고, 투자율, 전력손실, 수축률, 코아로스를 측정하였다.

• Journal of Korean Dental Science
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• 제3권2호
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• pp.20-25
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• 2010

Aim : This study was conducted to assess the oral health status of deaf and mute children attending special school. Materials and Methods : A cross-sectional descriptive survey was conducted among 137 deaf and mute children with ages ranging from 7 to 18 years. A total of 76 males (55.47%) with mean age of $14.2{\pm}4.5$ and 61 females (44.53%) with mean age of $13.8{\pm}4.2$ years and studying in a school for deaf and mute children in Warora were considered. Data were collected using a standard method recommended by WHO for the oral health survey in 1977. Oral health status was assessed using OHIS, Loe and Sinless, and CPI Index along with DMFT and DMFS Index. Gingival position was considered for measuring attachment loss. Statistical analysis was performed using the SPSS software package (version 17.0). Results : The mean DMFT was found to be $2.53{\pm}1.72$, and mean DMFS, $3.37{\pm}3.16$. The prevalence of dental caries was pegged at 35.32%, with mean OHIS score at $1.49{\pm}0.76$. Overall gingival index among deaf and mute children was $0.81{\pm}1.4$, whereas that for the upper arch and lower arch was $0.92{\pm}0.84$ and $1.19{\pm}0.95$, respectively. The mean score for the CPI Index among deaf and mute children was found to be $0.42{\pm}0.32$. Gingival clinical attachment loss was found to be $0.26{\pm}0.15mm$. Conclusion : These findings suggest that children with hearing disabilities can also have good oral hygiene comparable to normal individuals of the same age group. These results may be attributed to the fact that the study sample was taken from a single school of a private organization with a well-equipped dental setup.

• Journal of Periodontal and Implant Science
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• 제23권2호
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• pp.345-351
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• 1993

Various alloplastic materials have been used on the periodontally diseased ossous defects. Hydroxyapatite, which is used the most common alloplastic material is a non-resorbable form of calcium phosphate and natural coral which is a biodegradable by carbonic anhydrase in osteoclast was introduced recently. The purpose of the present study was to evaluate the clinical effects of porous hydoxyapatite and natural coral on the human periodontal defects. Four males and three females who had adult periodontitis were selected for this study. The teeth that had similar bone loss radiographically and periodontal pocket deeper than 5mm were selected. Gingival recession, pocket depth, plaque index(Silness & Loe), sulcus bleeding index and tooth mobility (measured by Periotest$^{(r)}$) were examined before graft. Before insertion of alloplastic materials, the depth from CEJ to bone crest and from CEJ to base of the osseous defect was recorded. Porous particulate hydroxyapatite(Interpore 200$^{(r)}$, A group) was place on the defect and natural coral(Biocoral$^{(r)}$, B group) was placed on the defect of the opposing tooth. Six months post-surgically the same parameters were recorded by reentry procedures. A and B group showed 0.6mm of mean recession. Mean reduction of pocket depth were 5mm for A group and 4.9mm of B group. Reduced SBI and tooth mobility were recorded. Osseous defect fills of the original defects were 2.9mm for A and 3mm for B group. Percentage defect fills were 71% for A and 59% for B group. The difference of defect fill between pre- and post-insertion was statstically significant(p<0.05). But the difference between the two groups was not significant statistically(p<0.05). The clinical impression at 6 month re-entry and the numerical date indicate that natural coral as well as porous particulate hydoxyapatite has a definite potential as an alloplastic implant in the treatment of periodontal osseous defects.

• 치위생과학회지
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• 제8권4호
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• pp.395-401
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• 2008

본 연구는 인구사회학적 특성 및 건강행위 특성과 치주상태의 관련성을 평가하여 치주건강 증진에 도움이 될 수 있는 기초자료를 제공하고자 실시되었으며 다음과 같은 결과를 얻었다. 1. 치면세균막지수 및 치은염지수는 인구사회학적 특성 및 건강행위 특성별 차이가 나타나지 않았다. 2. 치주낭보유분악수는 인구사회학적 특성에서 남자(3.34)가 여자(2.43)에 비해 높았으며(p < 0.01), 직무분야인 생산직(3.69), 전문직(3.43), 관리직(2.92), 가정주부(2.67), 사무직(2.61)간에서도 차이가 나타났다(p < 0.05). 건강행위 특성에서 흡연자(3.38)가 비흡연자(2.72)보다 유의하게 높았고, 음주횟수인 주 3회이상(3.48)과 주 2회 이하(3.32), 거의 마시지 않음(2.70) 사이에서도 차이가 확인되었다(p < 0.05). 3. 치간골소실량은 인구사회학적 특성에서 남자(71.79mm)가 여자(42.24 mm)에 비해 높았고, 직무분야로는 전문직(99.20 mm)이 매우 높았으며, 관리직(71.19mm), 생산직(61.07mm), 가정주부(50.86mm), 사무직(50.35mm)간에 높은 차이가 나타났다(p < 0.05). 건강행위 특성에서는 흡연자(67.23 mm)가 비흡연자(48.22 mm)보다 높은 상실율을 나타냈다(p < 0.05). 4. 상실치아수는 인구사회학적 특성에서 50대(0.74), 40대(0.35), 30대(0.17)간의 유의한 차이가 있었으며, 건강행위 특성에서는 음주횟수에서 주 3회 이상(0.68)과 주2회 이하(0.45), 거의 마시지 않음(0.20) 사이에 차이가 확인되었다(p < 0.05).